Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
2000-02-04
2003-10-21
Cangialosi, Salvatore (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S506000
Reexamination Certificate
active
06636531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication device and method for transmitting a sequence of data applied thereto at a certain transmission rate over a transmission line (or channel) that accommodates a larger transmission rate.
2. Description of the Prior Art
Recent years have seen the increasing use of image communication with the increasing capacity of networks and as image processing techniques grow more sophisticated. Especially, as for images, an image compression technique called MPEG-2, which is defined by International Standard ISO/IEC (International Organization for Standardization/International Electrotechnical Commission) 13,818, springs into wide use. There are two kinds of transmission formats that conform to MPEG-2; program streams (or PS) and transport streams (or TS). Transport streams constructed of 188-byte fixed-length packets come into wide use in transmission media such as satellite digital broadcasting and ground wave digital broadcasting.
In communications, there exist asynchronous transfer mode (or ATM), local area networks (or LAN), dedicated (or leased) lines such as a T
1
network and a digital signal level
3
(or DS
3
) network defined by American National Standards Institute or ANSI, and so on, as transmission lines. How to bear MPEG-2 TS streams over such a communication network (this is referred to as mapping) is an important issue in the use of the communication network for digital TV broadcasting.
Referring next to
FIG. 17
, there is illustrated a block diagram showing the structure of a prior art communication device and method for mapping MPEG-2 TS streams into DS
3
frames and for transmitting them over a DS
3
network, which is widely used mainly in North America. In the figure, reference numeral
1
denotes a communication device, numeral
2
denotes an MPEG-2 TS generating device, numeral
19
denotes an MPEG over ATM mapping unit, numeral
20
denotes a physical layer convergence protocol (or PLCP) framing unit, numeral
7
denotes a multiplexer, numeral
8
denotes a line coding unit, and numeral
10
denotes a system control unit for controlling the whole of the communication device
1
.
FIG. 18
is a diagram showing a method of mapping MPEG-2 TS streams into ATM cells, and
FIG. 19
is a diagram showing the structure of a PLCP frame that is constructed when mapping ATM cells into the DS
3
network channel.
In operation, MPEG-2 TS generating device
2
generates. MPEG-2 TS data constructed of 188-byte fixed-length packets based on information from a video source, and then sends out the MPEG-2 TS data to the communication device
1
. The MPEG-2 TS data is then furnished to the MPEG over ATM mapping unit
19
.
The MPEG over ATM mapping unit
19
divides each 188-byte MPEG-2 TS into four or more parts and then maps each of them into the 48-byte payload of each of four or more ATM cells. This mapping method is defined by Audio/Visual Multimedia Services: Video on Demand v1.1, which is a standard established by ATM Forum that is the ATM LAN standardization group in U.S.A. According to the standard, 384 bytes of data obtained by adding an 8-byte trailer defined by the ATM adaptation layer type
5
(or AAL
5
) to two MPEG-2 TS packets of 376 bytes is mapped into the payload of eight ATM cells.
Those ATM cells into which MPEG-2 TS data has been mapped in the above-mentioned way are then furnished to the PLCP framing unit
20
. The PLCP framing unit
20
performs a PLCP framing operation, as shown in
FIG. 19
, on the received ATM cells. The PLCP framing method of mapping ATM cells into frames to be transmitted over the DS
3
network channel is defined by ATM User-Network Interface Specification V3.1 which is a standard established by ATM Forum. According to the standard, twelve ATM cells are mapped into one PLCP frame to be transmitted at a frame rate of 125 microseconds. The difference between the transmission rate for MPEG-2 TS and that for the DS
3
network channel can be adjusted by inserting an idle cell as an ATM cell into each frame.
The multiplexer
7
then multiplexes PLCP frames generated by the PLCP framing unit
20
and a group of DS
3
headers generated by the DS
3
header generating unit
4
to generate DS
3
frames, and then sends out them to the line coding unit
8
. Each DS
3
frame is 4760 bits in length. And, each DS
3
frame has such a frame structure that it is divided into seven 680-bit sub-frames. Furthermore, each of the plurality of sub-frames is constructed of eight 85-bit blocks each of which includes a one-bit DS
3
header at the head thereof. The transmission rate for the DS
3
network channel is 44.736 Mb/s.
The line coding unit
8
performs a line coding operation on the DS
3
frames generated by the multiplexer
7
, and then sends out the line coded DS
3
frames over the DS
3
network channel. As the line coding, a kind of alternate mark inversion (or AMI) coding called bipolar with three zero substitution or B3ZS coding is used. The system control unit
10
controls the whole of the communication device
1
.
As previously mentioned, the prior art communication device
1
can map MPEG-2 TS streams into DS
3
frames to be transmitted over the DS
3
network channel so as to transmit the MPEG-2 TS streams by combining the MPEG over ATM technique with the PLCP framing technique.
A problem with the prior art communication method and device constructed above is that since much time is spent in performing the two steps of mapping MPEG-2 TS data into ATM cells first, and then mapping the ATM cells into PLCP frames, in order to transmit the MPEG-2 TS data over the DS
3
network channel, the delay is increased, and the complicated format processing required for carrying out the two steps increase the size of circuitry that implements the communication device.
In addition, mapping MPEG-2 TS data into ATM cells and further mapping them into PCLP frames can increase the overhead for the system, and therefore the transmission rate for MPEG-2 TS data that the network can accommodate is restricted with respect to the transmission band of the network. In other words, the utilization factor of the network is reduced. Since the difference between the transmission rate for MPEG-2 TS and that for the DS
3
network channel must be adjusted by inserting an idle cell as an ATM cell into each PLCP frame, MPEG-2 TS data cannot be distributed uniformly with respect to time during the transmission over the DS
3
network channel. In other words, there easily cause variations in the transmission of MPEG-2 TS data, such as a burst of data transmission, over the DS
3
network channel.
SUMMARY OF THE INVENTION
The present invention is made to overcome the above problems. It is therefore an object of the present invention to provide a communication method and device for mapping a sequence of data, such as MPEG-2 TS data, into frames to be transmitted over a network, such as a DS
3
network, the method and device being capable of reducing the delay caused by the mapping, improving the utilization factor of the network, reducing variations in the data rate that can occur during the transmission of MPEG-2 TS data over the network, and reducing the size of the circuitry that implements the communication device.
In accordance with one aspect of the present invention, there is provided a communication method for transmitting a sequence of data, which is transmitted thereto at a given transmission rate, at a desired transmission rate greater than the former transmission rate, the method comprising the steps of: in order to map the sequence of data into a plurality of frames in a predetermined form, each of which consists of a plurality of blocks, assigning a predetermined amount of data to a data transmission area in each of the plurality of blocks included in each frame so that the sequence of data is nearly-uniformly arranged over the plurality of blocks included in each frame; providing a stuff area for a predetermined one of the plurality of blocks included in each frame and determining
Hikino Shin
Nakashima Koichi
Birch, Stewart, Kolasch, & LLP.
Cangialosi Salvatore
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